Many complex electronic equipments are constructed of a number of discrete circuit modules in the form of printed circuit boards having circuit paths formed on each side to which may be connected various electrical components. Interconnections between circuit paths on opposite sides of the boards are accomplished by plated through holes. The plated through holes also function as receptacles for leads emanating from the electrical components. In the automated manufacturing of the boards, electrical components are inserted into the boards through the plated through holes by a component insertion machine. The component leads are then cut and cinched by the insertion machine, and then typically a visual check is made to ensure that component leads are present in predetermined holes. The boards then go through a soldering stage wherein the component leads are soldered to the board. Presently, only after the component leads are soldered, i.e. positive electrical connections are established between component leads and circuit paths, can electrical circuit testing be done to determine whether the right components have been inserted, whether the component is correctly oriented, whether the component is operable and whether the component meets the required circuit specifications.
When a defect is detected during the electrical testing, the defective part or parts have to be unsoldered which may damage the board and other components which are located nearby. Such a repair operation is very labor intensive and requires a relatively high labor grade personnel to perform. Because of the difficulty of repair of the boards after soldering, it has been recognized for a long time that it would be advantageous to perform electrical circuit testing on the board before the components are soldered to the board.
The problem, however, in performing electrical testing before component leads are soldered to the board is that there is no way to ensure that the components on the board are in fact electrically interconnected by predetermined circuit paths on the board. Consequently, a test result may indicate a defect with a component or circuit where in fact the problem may be caused by a poor or a complete absence of electrical connection between component leads and circuit paths on the board.